With the rapid growth of mobile communications and great progress of technology, the world will move towards a fully interconnected network society where anyone or any device can acquire information and share data anytime and anywhere. It is estimated that there will be 50 billion interconnected devices by 2020, of which only about 10 billion may be mobile phones and tablet computers. The rest are not machines communicating with human beings but machines communicating with one another. Therefore, the subject of how to design a system that better supports the Internet of Everything needs to be studied further.
In the standard of Long Term Evolution (LTE) of the Third Generation Partnership Project (3GPP), machine-to-machine communication is called machine type communication (MTC). MTC is a data communication service that does not require human participation. Deployment of large-scale MTC user equipments can be used in such fields as security, tracking, billing, measurement, and consumer electronics, and specifically relates to applications, including video monitoring, supply chain tracking, intelligent meter reading, and remote monitoring. MTC requires lower power consumption and supports lower data transmission rate and lower mobility. The current LTE system is mainly for man-to-man communication services. The key to achieving competitive advantages of scale and application prospects of MTC services is that the LIE network supports low-cost MTC devices.
In addition, some MTC user equipments need to be installed in the basement of a residential building or at a position within the protection of an insulating foil, a metal window, or a thick wall of a traditional building; MTC suffers from more serious and obvious penetration losses from air interfaces, compared to that of conventional equipment terminals (such as mobile phones and tablet computers) in LTE networks. 3GPP decides to study the project design and performance evaluation of MTC equipments with an additional 20 dB coverage enhancement. It should be noted that MTC equipments located in an area with poor network coverage have the Wowing characteristics: extremely low data transmission rates, low latency requirements, and limited mobility. In view of the above characteristics of MTC, the LTE network can further optimize some signals and/or channels to better support MTC services.
Therefore, at the 3GPP RAN #64 plenary session held in June 2014, a new MTC work item with low complexity and enhanced coverage for Rel-13 was proposed (see non-patent literature: RP-140990 New work Item on Even Lower Complexity and Enhanced Coverage LTE UE for MTC, Ericsson, NSN). In the description of this work item, an LTE Rel-13 system needs to support uplink/downlink 1.4 MHz RF bandwidth for an MTC user equipment to operate at any system bandwidth (for example, 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, or 20 MHz). The standardization of the work item will be completed at the end of 2015.
In addition, for better implementation of the Internet of Everything, at the 3GPP RAN #69 plenary session held in September 2015, a new work item was further proposed (see non-patent literature: RP-151621 New Work Item: NarrowBand IOT (NB-IOT), which may be called narrowband Internet of Things (NB-IOT). In the description of this item, NB-IOT needs to support uplink/downlink 180 KHz RF bandwidth and three modes of operation: stand-alone mode of operation, guard-band mode of operation, and in-band mode of operation. The stand-alone mode of operation is to implement NB-IOT on the existing GSM band. The guard-band mode of operation is to implement NB-IOT on the guard band of one LIE carrier. The in-band mode of operation is to implement NB-IOT on the existing LTE band. Different bearer modes may adopt different physical parameters and processing mechanisms.
In the existing LTE system, an LTE user equipment (UE) implements data transmission through a service request process. In the service request process, a base station (eNB) first acquires UE context information from a core network (CN) and saves it locally, and then sends a radio resource control (RRC) connection reconfiguration message to the UE to establish a data radio bearer (DRB), and data is transmitted through the data radio bearer. In an NB-IoT system, a UE in an RRC IDLE state needs to transmit only a small amount of data (small data) in one RRC connection. If small data is transmitted using the existing LIE data transmission process, the utilization rate of radio resources will be lowered. In order to reduce signaling overheads, the SA2 working group arrives at the following two solutions applicable to small data transmission: (1) a control plane data transmission manner (CP solution for short) based on non-access stratum (NAS) messages: in this solution, data is encapsulated in an NAS message packet data unit (NAS PDU) and transmitted to a receiving end through a signaling radio bearer (SRB). (2) A user plane data transmission manner (UP solution for short) based on access stratum context information stored in an eNB: in this solution, access stratum context information is established in an eNB and a data bearer is established, and data is transmitted and sent to a receiving end through the data radio bearer. Meanwhile, SA2 also concludes that the CP solution is a solution that must be implemented in a product, while the UP solution is an optional implementation solution.
For narrowband systems such as NB-IOT, eMTC, and MMTC, different service types usually require data transmission with different reliabilities. In the CP solution, data is encapsulated in an NAS message and transmitted on an SRB. In the existing LTE system, the SRB provides reliable data transmission based on a radio link control acknowledged mode (RLC AM). For service types requiring low reliability the CP solution based on the RLC AM causes large signaling overheads and low resource utilization rate. Therefore, the CP solution needs to provide data transmission services with different reliabilities for different service types.